A steering angle sensor (SAS) is an important component in an advanced automobile driving and control system. Its function is to measure the steering angle and the angular velocity of the steering wheel. The output of an ideal SAS shall indicate the possible rotational range of the steering wheel, which is +/−2.5 turns, or equivalently +/−900 degrees. The information of the angular velocity of the steering wheel, which is useful for the safety control of the vehicle, should be provided as well. As regard the environment for operation, a SAS should be able to tolerate the harsh condition in an automobile, which includes vibration, high humidity and temperature up to 80 degree C. In addition to the environmental requirement, a SAS shall be able to work properly with the unregulated battery power available in the vehicle, which might vary from 8 to 30 Volts due to the variation of the engine operation. While mounted in the very restricted space, the SAS shall be designed to adopt various diameters of steering columns.
Among the above-mentioned requirements, the most severe challenge to the design of a SAS is the vibration induced from the running engine. The frequency of the fundamental and harmonic vibrations can be up to several kHz. Such vibrations can cause the dithering effect and ruin sensors of contact type installed on the steering column. Therefore angle sensors of contact type, such as plastic-conductive-film potentiometers, are not adequate for the SAS. Furthermore, due to the humid and dusty environment, the optical devices are not suitable, either.
Finally, the SAS shall be able to communicate with the Electronic Control Unit (ECU) of the vehicle. For example, the Control Area Network (CAN) is a popular protocol widely used in the communication within the vehicle. The SAS shall include communication port with the ECU.
FIG. 1 shows a structural schematic diagram of a SAS according to the prior art. As shown in the figure, a steering column 12 inserts into the center of a main gear 14, and drives said main gear 14 to turn. The main gear 14 drives a first gear 15 and a second gear 16, wherein the numbers of gear teeth between the two gears differ by one. A set of magnet 17 is installed at the centers of the first gear 15 and the second gear 16, respectively. Above the magnets 17, Hall-effect sensors 18 are used for sensing the rotary angles of the first gear 15 and the second gear 16. When the main gear 14 turns by θ degrees, the first gear 15 and the second gear 16 turn by φ1 and φ2 degrees, respectively. The numbers of gear teeth of the main gear 14, the first gear 15, and the second gear 16 make θ and (φ1-φ2) have a one-on-one mapping in the rotary range of 0˜1560 degrees. Thereby, the rotary angle of the main gear 14 can be deduced from the difference between the output angles of the first and the second gears 15, 16. The sensing range exceeds 360 degrees. A single chip is used for calculating the output angles of the SAS according to the prior art. In practice, there are other combinations of gears to achieve the same function.
The Hall-effect sensors 18 of the first and the second gears 15, 16 are used to be an absolute angle sensor. After assembly and setting up zero point, the output of the sensor is the absolute rotary angle of the main gear 14 (0˜1560 degrees, 0 degree is set at −2.5-th turn). The output of the sensor will not exceed 1560 degrees. If the rotary angle of the main gear 14 exceeds the range, the SAS will still have output. However, the user will not know that the output is false. If the sensing range needs to be expanded, the number of gear teeth has to be re-calculated.
At present, there exists another type of steering angle sensor, which is used in the electro-hydraulic controlled brake module. This type of sensors adopts two sets of potentiometers. By a 90-degree phase difference between the two potentiometers, the steering angle is resolved. On the other hand, there exists another steering angle sensor with a multi-turn potentiometer. The rotary angle of the multi-turn potentiometer exceeds 360 degrees. Currently, multi-turn contact potentiometers are available. The absolute angular sensing range can reach 3600 degrees, which can satisfy the functional demands of the SAS without using a gear box. Instead, it can be driven directly by the steering column 12. However, as mentioned above, the contact-type sensors are not adequate for the SAS used in the vehicle.
Current steering angle sensors mostly adopt optical encoders and complicated reducer means. For example, the U.S. Pat. No. 4,955,228 uses optical encoders and means as the rotary sensor. A small part of current steering angle sensors adopts non-contact linear Hall-effect sensors as the rotary sensor, such as the Japanese Patent Laid-Open Publication No. H11-287608, in which ratchets, worm shafts, and Hall-effect sensors are used to form the rotary sensor. The non-contact angle sensor for automobiles and motorcycles of Taiwan utility model No. M285694 adopts magnetic sensors and microprocessors to construct the rotary sensor. However, the utility model provides only a framework without describing methods for sensing multi-turn steering angles. Besides, it does not describe adopted types and quantities of the sensors either. To the best knowledge of the inventors, all the current steering angle sensors use two sets of angle sensors for sensing +/−2.5-turn of absolute angles.
Thereby, the present invention provides a steering angle sensor, which uses only a pair of simple gears for transmitting rotary angles from the steering column to the sensor. A single rotary sensor with a sensing range of 0˜360 degrees is used for sensing the rotation of the steering column.